1. Field of the Invention
The present invention relates to a method of removing a coating from an edge of a substrate such as a glass substrate, a semiconductor wafer or the like.
2. Description of the Relevant Art
The process of fomling an integrated circuit on a substrate includes the step of forming a photoresist film on the substrate by spreading a dropped photoresist solution uniformly over the substrate upon rotation of the substrate.
According to the above step of forming a photoresist film on the substrate, as shown in FIG. 5(a) of the accompanying drawings, the photoresist film, indicated by R, includes a thick edge portion R' deposited on an edge of the substrate, indicated by W. When the photoresist film R is removed after being etched, the thick edge portion R' is left on the edge of the substrate W. In subsequent steps, the remaining edge portion R' becomes a source of small contaminating particles which are deposited on the surface of the substrate W, resulting in a poor yield of integrated circuits. this problem also occurs in the formation of a SOG (Spin-On-Glass) film on a substrate.
There have heretofore been proposed various methods of removing a coating from an edge of a substrate. For example, methods of removing a photoresist film from an edge of a rectangular glass substrate are disclosed in Japanese laid-open patent publications Nos. 5-114555, 5-175117, and 5-200350, and methods of removing a photoresist film from an edge of a semiconductor wafer are disclosed in Japanese laid-open patent publications Nos. 5-166720 and 6-45302.
According to the methods disclosed in Japanese laid-open patent publications Nos. 5-114555 and 5-175117, a nozzle for ejecting a solvent to dissolve and remove a photoresist film is moved along an edge of a substrate.
The method disclosed in Japanese laid-open patent publication No. 5-200350 involves use of a nozzle for ejecting a solvent to dissolve and remove a photoresist film, which nozzle is positioned below a rectangular glass substrate. In operation, the solvent is applied from the nozzle to the reverse side of the rectangular glass substrate to remove a photoresist film from an edge thereof.
The method disclosed in Japanese laid-open patent publication No. 5-166720 includes a nozzle having a solvent dropping port and a gas supply port which are defined in an upper arm thereof and a suction port defined in a lower arm thereof. When the method is in operation, an edge of a semiconductor wafer, from which a photoresist film is to be removed, is positioned in the nozzle between the upper and lower arms thereof.
According to the method disclosed in Japanese laid-open patent publication No. 6-45302, a photoresist film on upper and lower surfaces of an edge of a semiconductor wafer is removed by a solvent ejected from nozzles positioned above and below the edge of the semiconductor wafer, and a photoresist film on an outer surface of the edge of the semiconductor wafer is removed by a rotary brush that is held against the outer surface of the edge of the semiconductor wafer.
As a solvent to dissolve and remove a photoresist film in the above methods of removing, there has widely been used propylene glycol monomethyl ether acetate, which is also used as a solvent for a photoresist film and has low toxicity and excels in safety, or a mixture of this and propylene glycol monomethyl ether.
In any of the above conventional arrangements, the dissolving solvent is continuously ejected from the nozzle, and hence a large amount of dissolving solvent is required to process the edges of substrates. Even when the ejected dissolving solvent is retrieved, the amount of retrieved dissolving solvent is relatively small, and the retrieved dissolving solvent is largely degraded. Therefore, the process of retrieving the ejected dissolving solvent is not cost-effective.
The efforts disclosed in the above publications except the method disclosed in Japanese laid-open patent publication No. 6-45302 fail to sufficiently remove the remaining photoresist film from the outer surface of the edge of the substrate, though they can remove the photoresist film from the upper and lower surfaces of the edge of the substrate. As a result, the thick edge portion R' partly remains on the outer surface of the edge of the substrate, as shown in FIG. 5(b) of the accompanying drawings, after the edge of the substrate has been cleaned by the methods disclosed in the former four publications. According to Japanese laid-open patent publication No. 6-45302, since the remaining photoresist film is scraped off the outer surface of the edge of the substrate by the rotary brush, the disclosed method requires two different removing mechanism, i.e., the nozzles and the rotary brush, and hence is complex in overall structure. Furthermore, the remaining photoresist film cannot completely be removed from the outer surface of the edge of the substrate by the rotary brush.
Additionally, the above conventional dissolving solvent has problems of failing to form a flat and vertical section of the photoresist film near an interface and leaving contaminating particles. These problems produce a harmful effect on subsequent steps.